enable hhvm tests, create coverage, upload coverage

Author: Stephan Wentz

.scrutinizer

@@ -0,0 +1,3 @@
+tools:
+    external_code_coverage:
+        timeout: 600    # Timeout in seconds.

.travis.yml

@@ -4,7 +4,11 @@ php:
   - 5.5
   - 5.6
   - 7
+  - hhvm
 
 before_script: composer install 
 
-script: vendor/bin/phpunit -c tests
+script: vendor/bin/phpunit -c tests --coverage-clover=coverage.clover
+
+after_script:
+  - sh -c 'if [ $(phpenv version-name) = "5.6" ]; then wget https://scrutinizer-ci.com/ocular.phar && php ocular.phar code-coverage:upload --format=php-clover cove      rage.clover; fi;'